Drawing On Science For Kids

EVOLUTION: Human Evolution

Commentary By Stephen S. Yaeger

According to the Theory of Evolution all living things evolved from a common ancestor. Humans, as

primates, are no exception. Primates are mammals having a rounded head with a flat face. Their brains are relatively large compared to body size as well as more complex than those of other mammals. (The brains of marine mammals are also complex and have a volume similar to primates.)

Primates have eyes in front of the head, have stereoscopic vision and can see color. They can determine depth and distances. Their hands and feet are flexible and are equipped with nails rather than claws. Most primate hands have an opposablethumb, which can be brought opposite the index finger. There are two groups of primates: prosimians and anthropoids. Tarsiers, aye-ayes, and lemurs are prosimians. They are small-bodied, tree dwelling animals, and are mostly nocturnal. Humans, apes and monkeys are anthropoids. Anthropoids have more complex brains than the prosimians giving them greater intelligence.

The fossil record shows that anthropoids separated into three groups including Old World monkeys of Africa, Europe and Asia and New World monkeys of South and Central America. The third group of primates is the hominoids, which include humans and apes. Apes first appeared about 8 mya (million years ago) in Africa. At some point in geologic time the hominoids diverged into two separate groups: apes and humans. Very early on the apes lived in trees, but due to environmental changes one group had to chance being attacked by predators by dropping to the ground to search for new food sources. Over a long period of time a series of mutations allowed future generations to move upright. This is known as

bipedal movement.

Walking on two legs allowed for the free movement of hands and legs, which is an obvious advantage over walking on all fours. These early bipedal hominoids eventually evolved into a humanlike primate known as a hominid. The fossil record of hominids is fairly complete giving scientists a pretty good picture of how they eventually evolved into modern humans.

In 1924 Raymond Dart unearthed a fossil primate skull in Africa. Based on an examination of the skull it was found that the foramen magnum, the hole in the skull where the spinal column enters, was not at the back of the skull, but rather at its bottom. Mammals walking on all fours have the hole at the back of the skull so that the top of the skull is directly in line with the spine. Bipedalism dictates that the hole be at the skull's bottom allowing for holding the head upright with the back of the skull in line with the spine.

The fossil, estimated to be 2 to 3 million years old, was named Australopithecus africanus (australis = southern, pithecus = ape) and had apelike and humanlike qualities. In 1974 paleoanthropologist Donald Johnson found another fossil skull. It was a primate that existed between 3 and 5 million years ago and was classified as Australopithecus afarensis (ultimately named "Lucy"). These early hominids were bipedal; had a small, apelike brain; and had apelike shoulders and forelimbs.

These qualities are an indication that the australopithecines spent much time in trees and some time on the ground as clumsy, upright-walking primates. Other australopithecines have been found over the years and based on the evidence it is generally agreed that bipedalism developed prior to the development of a larger brain. It's believed that the group died out about 1 million years ago.

This brings us to the origins of modern man and when he first made tools, developed culture, communicated with sound, and recognized the world around him.

A fossil skull, with primitive tools nearby, was found by the Leakeys in Africa. This specimen had a larger braincase than the former fossils and its teeth and jaws were much smaller. These qualities made the fossil more human-like than the earlier discoveries. The Leakeys named the species Homo habilis ("handy human"). Subsequent finds of the species were found with stone tools.

Dating revealed that H. habilis lived between 1.5 and 2 million years ago and was the first hominid to make and use stone tools for cutting off bits of meat from bones. In the years following, other hominid fossils, H. rudolfensis and H. ergaster were found adding to the evidence of human evolution. Another hominid fossil was found and is believed to have evolved from H. habilis. It had a larger brain than H. habilis and had a more humanlike face. The browridges are large, its jaw slopes back, and it lacks a chin. It's believed to have lived 1.6 mya. An important feature of this hominid is that it walked upright so it was named Homo erectus ("upright human"). Stone tools, charred bones, and hearths found in the vicinity of fossils suggest it was a hunter and the first hominids to make use of fire.

It migrated out of Africa spreading out into Asia and possibly Europe. It became extinct some 300,000 to 500,000 years ago after giving rise to hominids similar to modern humans.

Neanderthal man, Homo neanderthalensis,was an early human living some 35,000 to 230,000 years ago in Europe, Asia and the Middle East. He was a powerfully built, short statured human having thick bones and large faces with prominent noses. These were not the brutish beasts commonly depicted in movies and fiction as "cavemen." New evidence suggests that they were in fact intelligent hunters, culturally oriented, and probably developed religious views. Contrary to popular belief they most likely communicated through a spoken language. In 1983 a Neanderthal hyoid bone was found in a cave in Israel. This bone was virtually identical to that of modern humans. It is a small bone that holds the root of the tongue in place, implying that it allowed the ability to speak. It was once suggested that if you met a Neanderthal on the street, you may not even recognize him as other than a fellow human.

The fossil record gives evidence of the origin of our own species, Homo sapiens(homo = man, sapiens = wise). In 1818 fossils were found in a 27,000- 23,000 year old cave in France. They were identified as modern humans and were given the name, Cro-Magnon. They lived at the same time as Neanderthal man. The fossil evidence reveals that they were top-class hunters and evolved a spoken language. They were identical to modern humans in height, skull and teeth structure, as well as brain size. The Cro-Magnon people were excellent toolmakers and artists and were the forerunners of humans living today.

New fossil dates indicate that modern humans were in South Africa and the Middle East some 100,000 years before the appearance of the Neanderthals. Genetic evidence suggests that H. sapiens had an African origin as early as 200,000 years ago.

Because of their close proximity it was believed that, possibly, Neanderthal gave rise to the Cro- Magnon, but scientists now say that the Cro-Magnons didn't arise from the Neanderthal. They evolved as a separate and distinct group.

There is controversy surrounding the disappearance of Neanderthal. Some say that the Cro-Magnon people, due to their higher intelligence, just out-did the "caveman." Others suggest a blending of the two peoples through interbreeding resulting in the human character living today. But whatever the reason for the demise of Neanderthal both Neanderthal man and Cro-Magnon man belong to separate branches of human evolution with the latter producing the Michelangelos, DaVincis, Newtons, and Einsteins of the world. Questions/comments? E-mail Steve:Drawingonscience@aol.com.